Super 3 Watt Audio Power Amplifier

Here is superb mini audio power amplifier circuit diagram. It can be powered with 4.5 volt dc to 18 volts dc (maximum). This amplifier is based on TDA1015, Product of NXP Semiconductors formerly PHILIPS Semiconductors.

The TDA1015 is a monolithic integrated audio amplifier circuit in a 9-lead single in-line (SIL) plastic package. The device is especially designed for portable radio and recorder applications and delivers up to 4 watt in a 4 ohm load impedance. The very low applicable supply voltage of 3,6 V permits 6 V applications.

Optimised Semiconductor Noise Source

We have already published designs that use a transistor junction operating in Zener breakdown as a noise source. Anyone who has experimented with a reverse-biased transistor knows that the amplitude of the noise voltage generated in this manner is strongly dependent on the supply voltage. The variation between individual transistors is also rather large. An obvious solution is to use an adjustable supply voltage for the noise generator stage. A BC547B starts to break down at around 8V.

Supply Voltage Monitor

A circuit for monitoring supply voltages of ±5 V and ±12 V is readily constructed as shown in the diagram. It is appreciably simpler than the usual monitors that use comparators, and AND gates. The circuit is not intended to indicate the level of the inputs. In normal operation, transistors T1 and T3 must be seen as current sources. The drop across resistors R1 and R2 is 6.3 V (12 –5 –0.7). This means that the current is 6.3mA and this flows through diode D1 when all four voltages are present. However, if for instance, the –5 V line fails, transistor T3 remains on but the base-emitter junction of T2 is no longer biased, so that this transistor is cut off. When this happens, there is no current through D which then goes out.

Thermal Fan Controller, IC 741

This fan controller uses one or more ordinary silicon diodes as a sensor, and uses a cheap opamp as the amplifier. The circuit designed for 12V computer fans, as these are now very easy to get cheaply. These fans typically draw about 200mA when running, so a small power transistor will be fine as the switch. I used a BD140 (1A, 6.5W), but almost anything you have to hand will work just as well.

Circuit diagram:

 click for large image

Thermal Fan Controller Circuit Diagram

Source: ESP

230V White LED Lamp

Did it ever occur to you that an array of white LEDs can be used as a small lamp for the living room? If not, read on. LED lamps are available ready-made, look exactly the same as standard halogen lamps and can be fitted in a standard 230-V light fitting. We opened one, and as expected, a capacitor has been used to drop the voltage from 230 V to the voltage suitable for the LEDs. This method is cheaper and smaller compared to using a transformer. The lamp uses only 1 watt and therefore also gives off less light than, say, a 20 W halogen lamp. The light is also somewhat bluer. The circuit operates in the following manner: C1 behaves as a voltage dropping ‘resistor’ and ensures that the current is not too high (about 12 mA).

The bridge rectifier turns the AC voltage into a DC voltage. LEDs can only operate from a DC voltage. They will even fail when the negative voltage is greater then 5 V. The electrolytic capacitor has a double function: it ensures that there is sufficient voltage to light the LEDs when the mains voltage is less than the forward voltage of the LEDs and it takes care of the inrush current peak that occurs when the mains is switched on. This current pulse could otherwise damage the LEDs. Then there is the 560-ohm resistor, it ensures that the current through the LED is more constant and therefore the light output is more uniform.


There is a voltage drop of 6.7 V across the 560-Ω resistor, that is, 12 mA flows through the LEDs. This is a safe value. The total voltage drop across the LEDs is therefore 15 LEDs times 3 V or about 45 V. The voltage across the electrolytic capacitor is a little more than 52V. To understand how C1 functions, we can calculate the impedance (that is, resistance to AC voltage) as follows: 1/(2π·f·C), or: 1/ (2·3.14·50·220·10-9)= 14k4. When we multiply this with 12 mA, we get a voltage drop across the capacitor of 173 V. This works quite well, since the 173-V capacitor voltage plus the 52-V LED voltage equals 225 V. Close enough to the mains voltage, which is officially 230 V.

Power MOSFET Active Bridge Rectifier

The losses in a bridge rectifier can easily become significant when low voltages are being rectified. The voltage drop across the bridge is a good 1.5 V, which is a hefty 25% with an input voltage of 6V. The loss can be reduced by around 50% by using Schottky diodes, but it would naturally be even nicer to reduce it to practically zero. That’s possible with a synchronous rectifier. What that means is using an active switching system instead of a ‘passive’ bridge rectifier.

The principle is simple: whenever the instantaneous value of the input AC voltage is greater than the rectified output voltage, a MOSFET is switched on to allow current to flow from the input to the output. As we want to have a full-wave rectifier, we need four FETs instead of four diodes, just as in a bridge rectifier. R1–R4 form a voltage divider for the rectified voltage, and R5–R8 do the same for the AC input voltage. As soon as the input voltage is a bit higher than the rectified voltage, IC1d switches on MOSFET T3.

Low Cost 12V to 220V Inverter

Even though today’s electrical appliances are increasingly often self-powered, especially the portable ones you carry around when camping or holidaying in summer, you do still sometimes need a source of 230 V AC - and while we’re about it, why not at a frequency close to that of the mains? As long as the power required from such a source remains relatively low - here we’ve chosen 30 VA - it’s very easy to build an inverter with simple, cheap components that many electronics hobbyists may even already have.

Though it is possible to build a more powerful circuit, the complexity caused by the very heavy currents to be handled on the low-voltage side leads to circuits that would be out of place in this summer issue. Let’s not forget, for example, that just to get a meager 1 amp at 230 VAC, the battery primary side would have to handle more than 20 ADC!. The circuit diagram of our project is easy to follow. A classic 555 timer chip, identified as IC1, is configured as an astable multivibrator at a frequency close to 100 Hz, which can be adjusted accurately by means of potentiometer P1.

Circuit diagram:

Cheap 12V to 220V Inverter Circuit Diagram

3-30V 3A Adjustable DC Power Supply

A regulated power supply for all general circuits, Based on a stablized DC voltage of 30 volt
This power supply is meant as an auxiliary or as a permanent power supply for all common circuits based on a stabilized DC voltage between 3 and 30V provided that the consumption does not exceed 3A. Of course this power supply unit can also be used for other purposes. Be replacing the trimmer by a potentiometer, it may even be used as an adjustable power supply unit. A good quality heatsink must be used.

Picture of project:

3 TO 30 Volt 3 Ampere DC Power Supply

NiCd Battery Charger With Reverse Polarity Protection

Small and portable unit, Can charge multiple batteries at once
This NiCd battery Charger can charge up to 7 NiCd batteries connected in series. This number can be increased if the power supply is increased with 1.65V for each supplementary battery. If Q2 is mounted on a proper heatsink, the input voltage can be increased at a maximum of 25V. Unlike most of comercial NiCd chargers available on the market, this charger has a reverse polarity protection. Another great quality is that it does not discharge the battery if the charger is disconnected from the power supply.

Usually , NiCd batteries must be charged in 14 hours at a charging current equal with a tenth percent from battery capacity. For example, a 500 mAh is charged at 50 mA for 14 hours. If the charging current is too high this will damage the battery. The level of charging current is controlled with P1 between 0 mA – 1000 mA. Q1 is opened when the NiCd battery is connected with the right polarity or if the output terminals are empty. Q2 must be mounted on a heatsink. If you cannot obtain a BD679, then replace it with any NPN medium power Darlington transistor having the output parameters at 30V and 2A. By lowering R3 value the maximum output current can be increased up to 1A.

Circuit diagram:

NiCd Battery Charger With Reverse Polarity Protection

45 Watt Class-B Audio Power Amplifier

45W into 8 Ohm - 69W into 4 Ohm, Easy to build - No setup required
These goals were achieved by using a discrete-components op-amp driving a BJT complementary common-emitter output stage into Class B operation. In this way, for small output currents, the output transistors are turned off, and the op-amp provides all of the output current. At higher output currents, the power transistors conduct, and the contribution of the op-amp is limited to approximately 0.7/R11. The quiescent current of the op-amp biases the external transistors, and hence greatly reduces the range of crossover.

The idea sprang up from a letter published on Wireless World, December 1982, page 65 written by N. M. Allinson, then at the University of Keele, Staffordshire. In this letter, op-amp ICs were intended as drivers but, as supply voltages up to +/- 35V are required for an amplifier of about 50W, the use of an op-amp made of discrete-components was then considered and the choice proved rewarding.

The discrete-components op-amp is based on a Douglas Self design. Nevertheless, his circuit featured quite obviously a Class A output stage. As for proper operation of this amplifier a Class B output stage op-amp is required, the original circuit was modified accordingly. Using a mains transformer with a secondary winding rated at the common value of 25 + 25V (or 24 + 24V) and 100/120VA power, two amplifiers can be driven at 45W and 69W output power into 8 and 4 Ohms respectively, with very low distortion (less than 0.01% @ 1kHz and 20W into 8 Ohms).

This simple, straightforward but rugged circuit, though intended for any high quality audio application and, above all, to complete the recently started series of articles forming the Modular Preamplifier Control Center, is also well suited to make a very good Guitar or Bass amplifier. Enjoy!

Circuit diagram:

45W Class-B Amplifier Circuit Diagram

NiMh and NiCd Battery Charger

This automatic NiCd charger for 9V NiCd batteries is using 555 timer properties and is very easy to build. Why is an automatic 9 volts NiCd battery charger? Because you can leave the battery for charging as much as you like: it will be always completely charged and ready for use when is needed. It wont be overcharged and it will not discharge. With the values presented in the circuit diagram, the battery charger NiCd circuit is suitable for 6V and 9V batteries.

Mobile Phone Travel Charger

Charge Your Mobile Phone While Enjoying The Journey
Here is an ideal Mobile charger using 1.5 volt pen cells to charge mobile phone while traveling. It can replenish cell phone battery three or four times in places where AC power is not available. Most of the cellphone batteries are rated at 3.6 V/500 mA. A single pen torch cell can provide 1.5 volts and 1.5 Amps current. So if four pen cells are connected serially, it will form a battery pack with 6 volt and 1.5 Amps current. When power is applied to the circuit through S1, transistor Q1 conducts and Green LED lights.

When Q1 conducts Q2 also conducts since its base becomes negative. Charging current flows from the collector of Q1. To reduce the charging voltage to 4.7 volts, Zener diode D2 is used. The output gives 20 mA current for slow charging. If more current is required for fast charging, reduce the value of R4 to 47 ohms so that 80 mA current will be available. Output points are used to connect the charger with the mobile phone. Use suitable pins for this and connect with correct polarity.

Circuit diagram:

Mobile Phone Travel Charger

Plant Watering Watcher

A flashing LED signals the necessity to water a plant, 3V powered circuit
This circuit is intended to signal when a plant needs water. A LED flashes at a low rate when the ground in the flower-pot is too dry, turning off when the moisture level is increasing. Adjusting R2 will allow the user to adapt the sensitivity of the circuit for different grounds, pots and probe types.

Improvements:
This little gadget encountered a long lasting success amongst electronics enthusiasts since its first appearance on this website in 1999. Nevertheless, in the correspondence exchanged during all these years with many amateurs, some suggestions and also criticism prompted me to revise thoroughly the circuit, making some improvements requiring the addition of four resistors, two capacitors and one transistor.

12V Speed Controller Dimmer

This handy circuit can be used as a speed controller for a 12V motor rated up to 5A (continuous) or as a dimmer for a 12V halogen or standard incandescent lamp rated up to 50W. It varies the power to the load (motor or lamp) using pulse width modulation (PWM) at a pulse frequency of around 220Hz.

SILICON CHIP has produced a number of DC speed controllers over the years, the most recent being our high-power 24V 40A design featured in the March & April 2008 issues. Another very popular design is our 12V/24V 20A design featured in the June 1997 issue and we have also featured a number of reversible 12V designs.

Circuit looks like:

For many applications though, most of these designs are over-kill and a much simpler circuit will suffice. Which is why we are presenting this basic design which uses a 7555 timer IC, a Mosfet and not much else. Being a simple design, it does not monitor motor back-EMF to provide improved speed regulation and nor does it have any fancy overload protection apart from a fuse. However, it is a very efficient circuit and the kit cost is quite low.

USB Power Injector For External Hard Drives

A portable USB hard drive is a great way to back up data but what if your USB ports are unable to supply enough "juice" to power the drive? A modified version of the Silicon Chip Usb Power Injector is the answer. For some time now, the author has used a portable USB hard drive to back up data at work. As with most such drives, it is powered directly from the USB port, so it doesn’t require an external plug pack supply.

Automatic Loudness Control

Simple add-on module, Switchable "Control-flat" option

In order to obtain a good audio reproduction at different listening levels, a different tone-controls setting should be necessary to suit the well known behavior of the human ear. In fact, the human ear sensitivity varies in a non-linear manner through the entire audible frequency band, as shown by Fletcher-Munson curves.

A simple approach to this problem can be done inserting a circuit in the preamplifier stage, capable of varying automatically the frequency response of the entire audio chain in respect to the position of the control knob, in order to keep ideal listening conditions under different listening levels.

Fortunately, the human ear is not too critical, so a rather simple circuit can provide a satisfactory performance through a 40dB range. The circuit is shown with SW1 in the "Control-flat" position, i.e. without the Automatic Loudness Control. In this position the circuit acts as a linear preamplifier stage, with the voltage gain set by means of Trimmer R7.

Switching SW1 in the opposite position the circuit becomes an Automatic Loudness Control and its frequency response varies in respect to the position of the control knob by the amount shown in the table below. C1 boosts the low frequencies and C4 boosts the higher ones. Maximum boost at low frequencies is limited by R2; R5 do the same at high frequencies.

Circuit diagram:

Automatic Loudness Controller Circuit Diagram

USB Powered Mobile Phone Battery Charger

Now you can charge your Mobile Phone from the USB outlet of PC
This simple circuit can give regulated 4.7 volts for charging a mobile phone. USB outlet can give 5 volts DC at 100mA current which is sufficient for the slow charging of mobile phones. Most of the Mobile Phone batteries are rated 3.6 volts at 1000 to 1300 mAh. These battery packs have 3 NiMh or Lithium cells having 1.2 volt rating. Usually the battery pack requires 4.5 volts at 300-500 mA current for fast charging.

But low current charging is better to increase the efficiency of the battery. The circuit described here provides 4.7 regulated voltage and sufficient current for the slow charging of the mobile phone. Transistor Q1 is used to give the regulated output. Any medium power NPN transistor like CL100, BD139, TIP122 can be used. Zener diode D2 controls the output voltage and D1 protects the polarity of the output supply. Front end of the circuit should be connected to a A type USB plug.

Connect a red wire to pin1 and black wire to pin 4 of the plug for easy polarity identification. Connect the output to a suitable charger pin to connect it with the mobile phone. After assembling the circuit, insert the USB plug into the socket and measure the output from the circuit. If the output is OK and polarity is correct, connect it with the mobile phone.

Circuit diagram:

USB Powered Mobile Phone Charger Circuit Diagram

Inverter Circuit For Soldering Iron

Here is a simple but inexpensive inverter for a small soldering iron (25W, 35W, etc) In the absence of mains supply. It uses eight transistors and a few resistors and capacitors. Transistors Q1 and Q2 (each BC547) form an astable multivibrator that produces 50Hz signal. The complementary outputs from the collectors of transistors Q1 and Q2 are fed to pnp Darlington driver stages formed by transistor pairs Q3-Q5 and Q4-Q6 (utilising BC558 and BD140).

The outputs from the drivers are fed to transistors Q7 and Q8 (each 2N3055) connected for push-pull operation. Use suitable heat-sinks for transistors Q5 through Q8. A 230V AC primary to 12V-0-12V, 4.5A secondary transformer (T1) is used. The centre-tapped terminal of the secondary of the transformer is connected to the battery (12V, 7Ah), while the other two terminals of the secondary are connected to the collectors of power transistors T7 and T8, respectively.

When you power the circuit using switch S1, transformer X1 produces 230V AC at its primary terminal. This voltage can be used to heat your soldering iron. Assemble the circuit on a generalpurpose PCB and house in a suitable cabinet. Connect the battery and transformer with suitable current-carrying wires. On the front panel of the box, fit power switch S1 and a 3-pin socket for connecting the soldering iron. Note that the ratings of the battery, transistors T7 and T8, and transformer may vary as these all depend on the load (soldering iron).

Circuit diagram:

Inverter Circuit Diagram For Soldering Iron

Bicycle Back Safety Light

Flashing 13 LED unit, 3V supply, Also suitable for jogger/walkers
This circuit has been designed to provide a clearly visible light, formed by 13 high efficiency flashing LEDs arranged in a pseudo-rotating order. Due to low voltage, low drain battery operation and small size, the device is suitable for mounting on bicycles as a back light, or to put on by jogger/walkers. IC1 is a CMos version of the 555 IC wired as an astable multivibrator generating a 50% duty-cycle square wave at about 4Hz frequency.

At 3V supply, 555 output (pin 3) sinking current operation is far better than sourcing, then LEDs D1-D6 are connected to the positive supply rail. In order to obtain an alternate flashing operation, a second 555 IC is provided, acting as a trigger plus inverter and driving LEDs D7-D12. D13 is permanently on. The LEDs are arranged in a two series display as shown below, with a center LED permanently on. This arrangement and the alternate flashing of the two series of LEDs provide a pseudo-rotating appearance.

Circuit diagram:

Bicycle Back Safety Light Schematic Circuit Diagram

Fading Leds

Two strips of LEDs fading in a complementary manner, 9V Battery-operated portable unit

This circuit operates two LED strips in pulsing mode, i.e. one LED strip goes from off state, lights up gradually, then dims gradually, etc. while the other LED strip does the contrary. Each strip can be made up from 2 to 5 LEDs at 9V supply. The two Op-Amps contained into IC1 form a triangular wave generator. The rising and falling voltage obtained at pin #7 of IC1 drives two complementary circuits formed by a 10mA constant current source (Q1, Q2 and Q5, Q6) and driver transistor (Q3 and Q6). R4, R5 & C1 are the timing components: the total period can be varied changing their values. R7 & R8 vary the LEDs brightness.

Circuit diagram:

Fading Leds Circuit Diagram

Dancing LEDs

LED sequencer: follows the rhythm of music or speech, 9V Battery-operated portable unit
The basic circuit illuminates up to ten LEDs in sequence, following the rhythm of music or speech picked-up by a small microphone. The expanded version can drive up to ten strips, formed by up to five LEDs each, at 9V supply. IC1A amplifies about 100 times the audio signal picked-up by the microphone and drives IC1B acting as peak-voltage detector. Its output peaks are synchronous with the peaks of the input signal and clock IC2, a ring decade counter capable of driving up to ten LEDs in sequence.

An additional circuit allows the driving of up to ten strips, made up by five LEDs each (max.), at 9V supply. It is formed by a 10mA constant current source (Q1 & Q2) common to all LED strips and by a switching transistor (Q3), driving a strip obtained from 2 to 5 series-connected LEDs. Therefore one transistor and its Base resistor are required to drive each of the strips used.

Circuit diagram:

Dancing LEDs Circuit Diagram

5V Regulated Power Supply

This circuit is a small +5V power supply, which is useful when experimenting with digital electronics. Small inexpensive wall tranformers with variable output voltage are available from any electronics shop and supermarket. Those transformers are easily available, but usually their voltage regulation is very poor, which makes then not very usable for digital circuit experimenter unless a better regulation can be achieved in some way.

The following circuit is the answer to the problem. This circuit can give +5V output at about 150 mA current, but it can be increased to 1 A when good cooling is added to 7805 regulator chip. The circuit has overload and thermal protection. The capacitors must have enough high voltage rating to safely handle the input voltage feed to circuit. The circuit is very easy to build for example into a piece of veroboard.


Circuit diagram:

5 Volt DC Power Supply Circuit Diagram

100W Inverter

Here is a 100 Watt inverter circuit using minimum number of components. I think it is quite difficult to make a decent one like this with further less components.Here we use CD 4047 IC from Texas Instruments for generating the 100 Hz pulses and four 2N3055 transistors for driving the load. The IC1 Cd4047 wired as an astable multivibrator produces two 180 degree out of phase 100 Hz pulse trains.

These pulse trains are preamplified by the two TIP122 transistors.The out puts of the TIP 122 transistors are amplified by four 2N3055 transistors (two transistors for each half cycle) to drive the inverter transformer.The 220V AC will be available at the secondary of the transformer. Nothing complex just the elementary inverter principle and the circuit works great for small loads like a few bulbs or fans.If you need just a low cost inverter in the region of 100 W, then this is the best.

Circuit diagram:

100 Watt Inverter Circuit Diagram

60 Watt Audio Power Amplifier

This project shows you how to build high quality 60 - 90W (into 4 Ohm load) powerful Amplifier. It suits for guitar or bass amplifier

To celebrate the hundredth design posted to this website, and to fulfil the requests of many correspondents wanting an amplifier more powerful than the 25W MosFet, a 60 - 90W High Quality power amplifier design is presented here. Circuit topology is about the same of the above mentioned amplifier, but the extremely rugged IRFP240 and IRFP9240 MosFet devices are used as the output pair, and well renowned high voltage Motorola's transistors are employed in the preceding stages.

The supply rails voltage was kept prudentially at the rather low value of + and - 40V. For those wishing to experiment, the supply rails voltage could be raised to + and - 50V maximum, allowing the amplifier to approach the 100W into 8 Ohm target: enjoy! A matching, discrete components, Modular Preamplifier design is available here: Modular Audio Preamplifier.

Automatic Low-Power Emergancy Light

Here is portable, simple and inexpensive unit white-LED-based emergency light that offers the following advantages. 1-It is highly bright due to the use of white LEDs. 2-The light turns on automatically when mains supply fails, and turns off when mains power resumes. 3-It has its own battery charger. When the battery is fully charged, charging stops automatically. The charger power supply section is built around 3-terminal adjustable regulator IC LM317 (IC1), while the LED driver section is built around transistor BD140 (Q2).

In the charger power supply section, an input AC main is stepped down by T1 to deliver 9V, 500mA to the bridge rectifier, which comprises diodes D1 through D4. Filter capacitor C1 eliminates ripples. Unregulated DC voltage is fed to input pin 3 of IC1 and provides charging current through D5 and limiting resistor R15. By adjusting preset P1, the output voltage can be adjusted to deliver the required charging current. When the battery gets charged to 6.8V, D6 conducts and charging current from IC1 finds a path throughQT1 to ground and it stops charging of the battery. When mains power is available, the base of Q2 remains high and Q2 does not conduct. Thus LEDs are off.

Flashing-LED Battery-status Indicator

Flashing-LED Battery-status Indicator will signals when an on-circuit battery is exhausted. It works with 5V to 12V operating voltage

A Battery-status Indicator circuit can be useful, mainly to monitor portable Test-gear instruments and similar devices. LED D1 flashes to attire the user's attention, signaling that the circuit is running, so it will not be left on by mistake. The circuit generates about two LED flashes per second, but the mean current drawing will be about 200µA. Transistors Q1 and Q2 are wired as an uncommon complementary astable multivibrator: both are off 99% of the time, saturating only when the LED illuminates, thus contributing to keep very low current consumption.

Circuit operation:

The circuit will work with battery supply voltages in the 5 - 12V range and the LED flashing can be stopped at the desired battery voltage (comprised in the 4.8 - 9V value) by adjusting Trimmer R4. This range can be modified by changing R3 and/or R4 value slightly. When the battery voltage approaches the exhausting value, the LED flashing frequency will fall suddenly to alert the user. Obviously, when the battery voltage has fallen below this value, the LED will remain permanently off. To keep stable the exhausting voltage value, diode D1 was added to compensate Q1 Base-Emitter junction changes in temperature. The use of a Schottky-barrier device (e.g. BAT46, 1N5819 and the like) for D1 is mandatory: the circuit will not work if a common silicon diode like the 1N4148 is used in its place.

Circuit diagram:

Flashing-LED Battery-status Indicator Circuit Diagram